1. Field of the Invention
The present invention relates to a vertical sealing device for a vertical type forming, filling and closing machine for flexible packages, and more particularly, to a vertical sealing device for appropriately controlling the timing of starting or halting a vertical sealing, i.e., center sealing of a cylindrical packaging material when the operation of the packing machine is stopped or restarted.
2. Description of the Related Art
As disclosed in, e.g., Japanese Patent Application Laid-open No.H9-58623 and Japanese Patent Publication No.H5-75616, the above-described type vertical sealing devices include a feed unit of a packaging material and a center heat sealer of the packaging material, and the operation and halting of the feed unit and the center heat sealer are electrically controlled.
The operation of the packing machine is maintained as long as the filling operation of articles into the packaging material is repeated at constant intervals. However, when there are not articles to be filled or the filing of the articles is failed, the operation of the packing machine is stopped. Thereafter, if the filling operation of articles is normally carried out, the operation of the packing machine is also restarted.
Even during a period of transition of the operation of the packing machine when the operation thereof is stopped or restarted, it is necessary to optimally control the feeding operation and the vertical sealing operation of the packaging material in order to prevent defective packaged products from producing. For this reason, both the sealing devices employ an unique control system for the feeding and center sealing of the packaging material during the period of transition of the operation of the packing machine.
In the case of the former sealing device (Japanese Patent Application Laid-open No.H9-58623), the operation of the packing machine is shifted to a transition period, one of the feed unit and the center heat sealer receives a halting signal or an operation signal therefor and then, the other of the feed unit and the center heat sealer receives a halting signal or an operation signal therefor after a predetermined delay time is elapsed therefrom. More specifically, when the operation of the packing machine is stopped, a halting signal is supplied to the feed unit first and then, after the feeding operation of the packing material by the feed unit is completely stopped, a halting signal is supplied to the center heat sealer. Therefore, until the packing material is completely stopped, the seam of superposed opposite side edges of the packing material is subjected to heat seal by the center heat sealer. On the other hand, when the operation of the packing machine is restarted, an operation signal is supplied to the center heat sealer, and after the heat seal of the seam is substantially restarted by the center heat sealer, an operation signal is supplied to the feed unit. Therefore, the seam of the packing material has already been subjected to the heat seal before the feed unit substantially feeds the packing material.
According to the above-described delay control, when the packing machine is stopped or restarted, the seam of the packing material can be subjected to the heat seal for sufficient time by the center heat sealer. Therefore, a portion of the seam of the packing material should not be insufficiently heated, i.e., faulty melting should not be occurred. As a result, it is possible to reliably carry out the center sealing with respect to the articles packed with packaging material.
The latter sealing device (Japanese Patent Publication No.H5-75616) employs a control system concerning the operation of the center heat sealer in which response delay is taken into consideration. More specifically, waiting time in which feeding operation of the packaging material by the feed unit is substantially at rest and response delay time required ON (close) and OFF (open) operation of the center heat sealer are compared with each other. If the response delay time is shorter than the waiting time, the OFF/ON operation of the center heat sealer is permitted. On the other hand, if the response delay time is longer than the waiting time, the OFF/ON operation of the center heat sealer is inhibited, and the center heat sealer is maintained in its ON state.
According to the latter sealing device, the OFF/ON operation of the center heat sealer is automatically controlled in accordance with the waiting time, i.e., the halting time. When the feeding operation of the packaging material is in a rest state for a long time, therefor, the center heat sealer should not be maintained in its ON state, and the seam should not be excessively heated, melted and ruptured.
However, in the case of the former sealing device, although fusion adhesion shortage of the seam of the packaging material can be avoided, a portion of the seam is heated twice by the center heat sealer, and excessive fusion adhesion of the seam is brought about. Such an excessive fusion adhesion disfigures the center seal, and degrades outer appearance quality of the packaged products.
Further, when the operation of the packing machine is stopped or restarted, it is desirable to decelerate or accelerate of the packaging material by the feed unit as gently as possible. If the packaging material is decelerated or accelerated gently, the center seal should not be wrinkled. However, gentle deceleration and acceleration increase the heating time of the seam of the packaging material, which brings about excessive fusion adhesion.
On the other hand, in the latter sealing device, if the above-mentioned waiting time of the packaging material is short, the center heat sealer is maintained in its ON operation. In this case, the deceleration and the acceleration of the packaging material increase the heating time of the seam of the packaging material, which also brings about excessive fusion adhesion.
It is an object of the present invention to provide a vertical sealing device for a packing machine, which does not bring about fusion adhesion shortage and excessive fusion adhesion in a center seal of a packaging material and which does not cause wrinkle in the center seal.
A vertical type packing machine with a vertical sealing device of the present invention includes a filling tube which guides a cylindrically formed packaging material and which is used for intermittently filling at least one article into the packaging material, the packaging material being formed such that both side edges thereof are superposed on each other so as to form a seam extending along the filling tube.
The vertical sealing device for achieving the above object comprises: a feed unit for feeding the packaging material along the filling tube, the feed unit including a constant mode for feeding the packaging material at a steady speed during a normally operating state of the packing machine, and a transition mode for feeding the packaging material at a speed other than the steady speed; a center heat sealer for heating and sealing the seam of the packaging material; and control means for controlling operation of the feed unit and the center heat sealer, the control means having a start timing for starting the operation of the center heat sealer, and a halt timing for halting the operation of the center heat sealer, and at least one of the start timing and halt timing being located in the transition mode of the feed unit.
According to the sealing device, the operation of the center heat sealer is halted after a predetermined time from the halt of operation of the feed unit when the operation of the packing machine is halted, or the center heat sealer is operated after a predetermined time from the start of operation of the feed units when the operation of the packing machine is restarted. Therefore, the seam of the packaging material should not be heated excessively or insufficiently, and it is possible to reliably prevent the fusion shortage or excessive fusion.
More specifically, the feed unit includes, as the transition mode, an acceleration mode for accelerating the packaging material from a halt state to the steady speed when the filling operation of the article into the packaging material is restarted from a halt state of the packing machine, and a deceleration mode for decelerating the packaging material from the steady speed to the halt state when a non-filling operation of the article occurs during the normally operation of the packing machine.
In this case, the control means has the start timing located in the acceleration mode, or has the halt timing located in the deceleration mode. More preferably, the control means may have he start timing and halt timing located in the acceleration and deceleration modes, respectively.
A period of time of each of the acceleration mode and the deceleration mode substantially may coincide with one packing cycle time required for forming one packaged products which contains the article during the steady operating state of the packing machine. In this case, the packaging material is gently accelerated and decelerated in the acceleration mode and the deceleration mode without largely lowering the packing ability of the packing machine. As a result, it is possible to effectively prevent wrinkles at the center seal.
Further, the feed unit may include, as the transition mode, temporary suspension regions in the acceleration mode and the deceleration mode, respectively. In this case, it is preferable that the packaging material is fed at the same speed in the temporary suspension regions.
If the feeding speed of the packaging material in the temporary suspension regions is the same, the control means can operate the feed unit continuously so as to directly shift the feeding state of the packaging material from the temporary suspension region in the deceleration mode to the temporary suspension region in the acceleration mode when a situation in which non-filling operation of the article does not occur continuously. In this case, the packing ability of the packing machine is not lowered substantially.
In such a state, the control means may have the start timing located after termination of the temporary suspension region in the acceleration mode, and may have the halt timing located within the temporary suspension region in the deceleration mode.
When no wrinkles at the center seal is more important than the packing ability of the packing machine, a period of time of the acceleration mode is set equal to or longer than the one packing cycle time, and a period of time of the deceleration mode is set equal to or shorter than the one packing cycle time.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirits and scope of the invention will become apparent to those skilled in the art from this detailed description.